Patients with the most impressive antimyeloma responses had the highest levels of blood CAR-BCMA⁺ cells. (A) CAR-BCMA⁺ PBMCs were quantified in the blood of patients by qPCR. Patients treated on the 2 lower dose levels had low levels of CAR-BCMA⁺ cells in their blood (left). Patients treated on the higher 2 dose levels had higher levels of CAR-BCMA⁺ cells in their blood (right). Patients 8, 10, and 11 had the best antimyeloma responses and the highest levels of blood CAR-BCMA⁺ cells. The results are presented as the absolute number of CAR⁺ PBMC/μL of blood. Pre stands for pretreatment. (B) IL-6 was measured in the serum of all patients. Patients 10 and 11 (right) had the most severe cytokine-release syndrome, and these patients also had the highest serum IL-6 levels. Serum IL-6 levels of the other patients are shown on the left. Note the different y-axis scales on the left and right graphs. (C) Five days after CAR-BCMA T cell infusion, serum levels of 15 cytokines were measured in the blood of patient 10 and patient 11. Results are expressed as fold increase over pretreatment levels. (D) Serum soluble BCMA of all patients was measured by ELISA pretreatment and posttreatment. The posttreatment serum samples were obtained 22 to 29 days after CAR T-cell infusion for all patients except patient 12. The posttreatment sample of patient 12 was obtained 13 days after CAR T-cell infusion. All patients had detectable serum BCMA. In the patients obtaining the most impressive antimyeloma responses, Patients 8, 10, and 11, serum BCMA decreased posttreatment (right); in contrast, serum BCMA did not decrease substantially posttreatment in the other patients (left).